Field of the Invention
The present invention relates to a method and an apparatus for fuel injection of an engine system. More particularly, the present invention relates to a method and an apparatus for fuel injection of an engine system that optimizes pilot injection in the engine system recirculating exhaust gas in a cylinder by a variable valve apparatus.
Description of Related Art
Generally, in order to reduce vibration/noise generated in an engine, pilot injection is introduced.
In the pilot injection, before an injector performs main injection for combustion, a predetermined amount of fuel is injected at a predetermined point in time so that temperature of a combustion chamber is raised and a mixture of fuel and air is improved. The pilot injection is performed at least once and may be multiply performed in accordance with a driving condition.
Through the pilot injection, ignition delay is reduced and a rate of increase of combustion pressure can be reduced. As the rate of increase of the combustion pressure is reduced, combustion noise can be reduced.
Furthermore, in order to implement an appropriate valve operation in accordance with the RPM of the engine, a Variable Valve Lift (VVL) apparatus that has a plurality of shapes of cams operating valves or that operates valves at different lifts in accordance with the RPM of an engine has been studied.
The engine provided in the variable valve apparatus may resupply exhaust gas exhausted from a combustion chamber to the combustion chamber by opening an exhaust valve during an intake stroke (hereinafter called ‘internal EGR (exhaust gas recirculation)’).
However, when the exhaust gas is recirculated to the combustion chamber through the variable valve apparatus, the temperature of the combustion chamber is changed, and the fuel amount and injection timing of the pilot injection should be changed. Therefore, when the exhaust gas is resupplied to the combustion chamber through the variable valve apparatus, it needs to optimize a combustion state through exactly controlling the fuel amount and the injection timing of the pilot injection.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.